The continuing development of the magnetic recording/reproducing device of the hard disk type is following the trend toward reduction in the diameter of the magnetic disk, reduction in the size and weight of the apparatus, and an increase in recording density. The higher the recording density of the magnetic disk becomes, the smaller is the distance (or flying height) between the magnetic disk and the magnetic head. It is expected in the near future that recording and reproducing will be accomplished in such a manner that the magnetic head is in complete contact with the magnetic disk. Then, the magnetic disk will be subject to a much severe sliding condition. On the other hand, an increase in recording density needs a smaller flying height and a smoother magnetic disk surface (for stable flying). The consequence is that the head slider (supporting the magnetic head) slides on (keeping in contact with) the magnetic disk for a longer period of time than before (sliding in this manner is referred to as contact sliding hereinafter), the disk is subject to more dynamic friction and wear than before during its start-up, and there occurs a limiting static friction (referred to as stiction hereinafter) between the head and the disk. The result of an increase in the dynamic friction and wear due to contact sliding is an occasional disk crash and head wear which tends to disable recording and reproducing operations. Moreover, strong stiction disables the start-up of the disk and damages the disk head.
In order to address the above-mentioned problems, there has been developed a magnetic disk of a new type which has two separate regions: one in which the head slider stands by when the magnetic disk is at rest and experiences contact start and contact stop when the disk starts and stops, and the other in which the head performs recording and reproducing while the disk is running. The former region is referred to as CSS region and the latter as a data region. The CSS region is usually formed in an inner section of the magnetic disk and it has its surface roughened so as to prevent stiction. By contrast, the data region has its surface smoothed so as to ensure a stable head floating. The magnetic disk having a CSS region and data region needs a special lubricating film and lubricating technologies. For example, Japanese Patent Laid-open No. 36277/1994 discloses a method of preventing stiction by forming a protuberance (about 5 nm high) on the rail surface of the slider in the CSS region. Also, Japanese Patent Laid-open No. 111292/1994 discloses the use of a liquid lubricant in the CSS region and a solid lubricant in the data region. These prior art technologies are directed to the lubricating film to be applied to the magnetic disk in which are formed the CSS region and data region, and the lubricating film realizes to some extent the sliding characteristics required of the CSS region and data region. There is a distinct difference in requirements between the lubricating film for the CSS region and the lubricating film for the data region because the head-disk sliding state differs in these two regions. In the CSS region, it is possible to somewhat reduce stiction by roughening the surface of the magnetic disk, but there is a need for a lubricating film with good durability because contact sliding takes place when the disk starts up and stops. In the data region, however, it is necessary that the disk have a small surface roughness and the lubricating film have a low stiction. The reason for this is that the head slider could come into contact with the data region (causing strong stiction) when the disk stops suddenly (due to some anomaly) while the head slider lies in the data region. Therefore, the lubricating film in the CSS region should differ in lubricating performance from that in the data region.
The lubricant now in use for magnetic disks is a perfluoropolyether compound having functional groups for adsorption to the disk surface. This lubricant gives rise to a lubricating film which is composed of a layer firmly adsorbed to the disk surface and a layer which is adsorbed weakly or not adsorbed to the disk surface. The firmly adsorbed lubricating layer does not separate from the disk surface when the disk is washed with a perfluorocarbon solvent. On the other hand, the weakly adsorbed lubricating layer is easily separated from the disk surface by washing. This weakly adsorbed lubricating layer, however, plays an important role in the CSS region which needs good durability, because it is necessary that the lubricant partly moves to the slide surface of the head slider at the time of sliding so that a stable frictional state is established. Without this weakly adsorbed layer in the CSS region, it is impossible to maintain satisfactory reliability. By contrast, the data region needs low stiction, because cohesion of the lubricant in the gap between the head and the disk should be avoided when the head comes into contact with the data region at the time of an anomalous sudden stop and the excessive scraping up of the lubricant by the head during seeking should be avoided. Thus, the weakly adsorbed layer, which is easily mobile on the disk surface, has an adverse effect on stiction contrary to durability. For this reason, the weakly adsorbed layer should be as little as possible. If a conventional lubricant of the adsorption type is applied to the entire surface of the disk and the data region alone is washed to remove the weakly adsorbed layer, it necessarily follows that the lubricating film in the data region decreases in thickness. At the present time, there is by far a smaller chance of contact sliding in the data region than in the CSS region; however, in the future magnetic disk apparatus in which the flying height of the head will decrease further, there will be a stronger chance of contact sliding between the head and disk even in the data region. Thus, there will be, in a near future, a demand for the data region to have good durability. This implies that the lubricating film in the data region should be thick enough to endure occasional contact sliding.
These technical problems are not solved completely by the above-mentioned prior art technologies. The technology disclosed in Japanese Patent Laid-open No. 111292/1994 provides the respective regions with the desired lubricating characteristics by coating the CSS region with a liquid lubricant and the data region with a solid lubricant. This technology suffers the disadvantage of requiring a complex process to form the lubricant films. The technology disclosed in Japanese Patent Laid-open No. 53027/1992 ensures low stiction in the data region and good durability in the CSS region by forming the lubricating films such that the lubricating film in the data region is thinner than the lubricating film in the CSS region. This technology, however, is not satisfactory because it is necessary to maintain a certain thickness for the lubricating film in the data region in order to ensure good durability. At the present time, there is no effective means to ensure satisfactory slide reliability for a disk having a CSS region and data region formed thereon.
The present invention was completed to address the above-mentioned problems involved in the prior art technology. It is an object of the present invention to provide an effective means to ensure satisfactory slide reliability for a disk having a CSS region and data region formed thereon. It is another object of the present invention to provide a high-performance magnetic disk and magnetic recording/reproducing device that employ such means.